In the process of manufacturing semiconductor devices, a semiconductor wafer is subjected to processes of various kinds, such as film-formation, oxidation, diffusion, annealing, reformation, and etching. Before the processes, there may be a natural oxide film (consisting of SiO2 if the wafer is Si) formed on the surface of the semiconductor wafer. The natural oxide film can cause the semiconductor devices to have lower electrical characteristics or to be defective. For this reason, a treatment of removing the natural oxide film from the surface of the semiconductor wafer, i.e., pre-cleaning, is performed before the processes.
Jpn. Pat. Appln. KOKAI Publication No. 2-256235 discloses an example of a method of the pre-cleaning. In this method, a natural oxide film on a semiconductor wafer is first converted into an intermediate that easily sublimes. Then, the wafer is heated to sublimate and remove the intermediate. The formation of the intermediate is performed in a first processing apparatus at a low process temperature, and the sublimation of the intermediate is performed in a second processing apparatus at a high process temperature.